This invention generally relates to a unitary container member and to a method and apparatus for molding same. More particularly, the present invention relates to a container member having an undercut or re-entrant sealing flange integrally formed with the body portion of the container member in order to provide a container member that has a sealing flange which does not project substantially beyond the external dimensions of the container member, and the container member is formed by a thermoforming molding apparatus according to this invention that includes a short-stroke gate in the flange-forming portion thereof, which gate breaks away for ready removal of the thermoformed container member, and particularly its undercut flange, from the molding apparatus.
Packaging assemblies such as the so-called blister packs that are in wide use today often include container members to which an end closure member or lid sheet is sealed onto a sealing lip of the container member after the product being packaged is inserted into the container member. These types of container members are typically made on molding machines such as those of the form-fill-seal type that include dies which thermoform sheets of rollstock into webs having a plurality of container members. Within such dies, a web of rollstock is heated to form a container member, the forming operation typically including vacuum pulling or air pressure formation of the heated rollstock web to the interior configuration of the dies, often an upper and lower die that define the mold cavity. After the container member is suitably formed within the mold cavity, the mold cavity is opened, usually by downward movement of the lower die member until it clears the bottom of the thermoformed container member, after which the thermoformed container member moves out of the molding cavity for subsequent processing or use.
At this stage, the container members remain in web form for ease of subsequent operations such as filling, sealing and the like, during which multiple container members of the web are subjected to such additional operations whereupon such operations are carried out simultaneously on the multiple container members of the web. While this feature of being able to carry out an operation simultaneously on multiple containers of the web enjoys numerous advantages of speed, efficiency and consistency, the molding of the container members must be carried out in such a manner that the container members can be removed from the molding cavity without dividing up or otherwise damaging the web. For example, it is typically required that the upper and lower die members of the molding cavity must be structured such that the container members formed in the web readily break loose of and clear the internal molding surfaces of the die members as the lower die drops with respect to the upper die. Generally speaking, this requirement is met when web-joined container members have side walls that include no undercut or re-entrant surface features that project inwardly with respect to the individual container members, it being understood that these side walls are the walls of the container member that lie along the direction of typically downward movement of the lower die member.
As a result, container members formed in this manner typically cannot have side walls that include internally projecting surface portions of any substantial length, such as undercut sealing flanges. Undercuts of some length and of certain configurations can sometimes be formed in the side walls of these types of containers by the use of retractable cores, resilient molding disks, retractable rods, angle pins, sliding blocks and the like. Moreover, these types of molding devices typically require significant separation of adjacent cavities or long-stroke operations, which can lead to substantial wastage of rollstock material.
Because of the limitations with respect to having substantial portions of the side walls or extensions thereof project inwardly, heretofore the sealing lip of these container members has been positioned to lie generally outside of or external to the side walls of the container member. The composite packaging assembly utilizing these container members includes a lip that projects well outside of or beyond the periphery of the side walls of the container member. Such packaging assemblies have an outside dimension that is far in excess of that actually needed to containerize the product being packaged, which increases the shipping and storage size of the packaging assembly. Also, since there is substantially no re-entrant or inwardly projecting portion of such conventional sealing lip structures, the side walls are virtually free of horizontal creases and are of no assistance in containment of the product within the packaging assembly or within the container member prior to sealing the closure lid thereto.
By the present invention, a container member is provided with a peripheral sealing flange that is undercut such that the sealing flange does not appreciably extend, in a direction away from the center of the container member, beyond the outermost perimeter of side walls of the container member. The sealing flange of the product aspect of this invention includes an undercut section that projects generally inwardly of the container member, which structure reduces the shipping and storage size of the container member while also providing an inwardly projecting surface that assists in retaining the product while it is being packaged and while it is being opened, especially when the product includes elongated resilient portions that must be folded upon themselves, such as tubing and the like. Containers having sealing flanges according to this invention tend to have improved stacking strength, and they also conserve rollstock materials in that it is possible to form additional container members for a given area of rollstock inasmuch as the container members can be formed at locations on the web that are more closely spaced from each other than when the sealing flanges project beyond the side walls of the container member.
The container member according to this invention is a unitary container member in which its body portion is integrally formed with its sealing flange and lip, the flange including a section that is undercut or re-entrant with respect to the side walls of the container member. Such a container member is formed by an improved thermoforming method and apparatus which provide a molding cavity that includes the use of a short-stroke gate assembly to define part of its flange-forming portion, which gate assembly opens to afford a generally unobstructed passageway out of the molding cavity in the leading direction, which is the direction that the web moves through the thermoforming apparatus, or the upstream direction.
Accordingly, it is a general object of this invention to provide an improved container member for a packaging assembly.
Another object of the present invention is to provide an improved container member having a re-entrant sealing flange, as well as the method and apparatus for molding same.
Another object of this invention is to provide an improved product that is thermoformed from a web of rollstock while forming side walls thereof that have generally internally projecting portions.
Another object of the present invention is to provide an improved product and an improved apparatus and method for making same which reduces the shipping and storage size of a container having a given volume.
A further object of this invention is to provide an improved product, and an improved apparatus and method for making same which includes a peripheral flange at the mouth thereof which has a re-entrant configuration that assists in retaining products within the container member.
Another object of this invention is to provide an improved thermoforming apparatus and method that selectively provides a clear pathway out of the molding cavity thereof in the upstream direction of movement of the leading edge of the web of stock material being thermoformed.
Another object of this invention is to provide an improved thermoforming method and apparatus that minimizes the area of rollstock that lies between container members thermoformed thereby.
Another object of this invention is to provide an improved thermoforming method and apparatus that utilizes a short-stroke gate assembly.